Safety and environmental considerations are forcing changes in printing ink formulations. Solvent-based printing inks are now regarded as being undesirable from several points of view and are being tolerated only because effective water-based printing ink compositions have not been developed to the point where they can replace solvent-based inks in terms of ease of use, printability and economy. This is particularly true for publication gravure printing inks which are generally based on toluene or mixtures of toluene and aliphatic hydrocarbons. Such solvents are hazardous (explosions at publication gravure printing plants have occurred in recent years) and require expensive solvent recovery units to limit air effluents (toluene and toluene/aliphatic hydrocarbon mixtures are very volatile, particularly at the temperature and air flow conditions normally present in printing press driers).
As a result of heightened environmental and safety concerns, water-based inks are being introduced to replace solvent-based inks. However, prior art water-based inks have proven to be expensive and prone to printability problems, especially for publication gravure. Examples of such printability problems include poor transfer from the gravure cells and spreading behavior on paper. These printability problems typically manifest themselves as skipped dots in the tone areas and a generally "wormy" appearance and nonuniformity in the solids. U.S. Pat. No. 4,954,556 relates to water-based ink compositions comprising emulsion polymers and rewetting agents. This patent alleges that the ink compositions described therein can be printed at high speed without permanent drying in the cells of a gravure cylinder, transfer of the ink composition to the substrate is not adversely affected and the inks dry quickly without causing paper curling. Although such qualities are most desirable, the ink compositions described in this patent are nevertheless disadvantageous because they contain extremely high (i.e. 10-50 wt.%) amounts of surfactant(s). Such high surfactant content leads to trapping problems on the paper, foaming problems during printing and, most importantly, very high cost. Unless these latter problems can also be overcome, there would be very little incentive for a printer to change from a solvent-based ink to such a water-based ink.